1. Field of the Invention
The present invention relates to a network system, and more particularly, to a method of transmitting or receiving one or more data packet in a Wavelength Division Multiplexing (WDM) based network system.
2. Discussion of the Related Art
As the current network technology based on an optical cable is widely used in many engineering fields, various methods of optimizing the signal transmission bandwidth of the optical cable are currently being aggressively researched. Some of the examples are Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), and Wavelength Division Multiplexing (WDM) techniques.
Among the methods mentioned above, the WDM technique deserves considerable attention because it is able to maximize the transmission bandwidth of the optical cable without having any drastic improvements of the existing electrical systems. The network system employing the WDM technique initially modulates each signal to a signal having a particular wavelength and transmits each modulated signals through an optical cable line.
FIG. 1 illustrates a network system employing the WDM method according to the related art. As shown in the figure, the system includes a star coupler 20 and a plurality of nodes 10. Each node includes a Wave Tunable Transmitter (hereinafter, “WTT) 31, a Wave Fixed Transmitter (hereinafter, “WFT”) 32, a Wave Tunable Receiver (hereinafter, “WTR”) 33, and a Wave Fixed Receiver (WFR) 34.
Each node of the network system employing the WDM technique transmits or receives a data packet to or from another in an asynchronous way. For example, if the node-A 13 desires to send a data packet to the node-C 11, the WTT 31 of the node-A 13 initially sends the wave information of the node-A 13 to the WFR 34 of the node-C 11.
Then the WTR 33 of the node-C 11 adjusts its packet-receiving channel in accordance with the wave information received. When the packet-receiving channel of the node-C 11 accords to the wave information of the node-A 13, the WFT 32 of the node-A 13 finally sends the data packet to the node-C 11.
In a case where the node-A 13 alone sends a packet to the node-C 11, the node-A is able to complete its packet transmission without any problem. However, if another node (e.g., node-B 12) has started to send a packet to the node-C 11 before the node-A 13 does, the WTR 33 of the node-C 11 adjusts its packet-receiving channel in accordance with the wavelength information given by the node-B 12. Therefore, the node-A 13 may not be able to access to the packet-receiving channel of the node-C 11. This results the lower efficiency of the whole network system.
In order to overcome the problem described above, each node of the system may transmits/receives a packet to/from another node using a synchronous process instead, in which the packet-receiving channel of a receiving node can be fixed.
However, this may cause another problem. In a case where a transmitting node having a first packet-receiving channel sends a normal packet to a receiving node having a second packet-receiving channel, one or more packets being unloaded from the first packet-receiving channel may collide with the normal packet being loaded into the second packet-receiving channel.